Reference intervals for indices derived from the complete blood count in the Longitudinal Study of Adult Health (ELSA-Brasil)

INTRODUCTION: Hematological biomarkers from routine tests are attractive for their accessibility and clinical applicability, particularly indices derived from the complete blood count. Establishing reference intervals is essential for accurate interpretation, requiring healthy populations and standardized methods following Clinical and Laboratory Standards Institute guidelines. OBJECTIVE: To establish reference intervals for complete blood count-derived indices in healthy adults. METHODS: This cross-sectional study analyzed baseline data from 2230 participants aged 35-74 years in the Brazilian Longitudinal Study of Adult Health. Individuals with inflammatory conditions or hematological extremes (<1st and >99th percentiles) were excluded. Evaluated cellular parameters comprised five inflammatory ratios (neutrophil-to-lymphocyte, platelet-to-lymphocyte, lymphocyte-to-monocyte, monocyte-to-lymphocyte, and derived neutrophil-to-lymphocyte) and three composite indices (systemic inflammatory response, aggregate index of systemic inflammation, and systemic immune-inflammation). Reference intervals corresponded to the 2.5th-97.5th percentiles. Group differences by sex and age were evaluated using Mann-Whitney and Harris-Boyd tests. RESULTS: Males constituted 54.3% of the sample, and 92.0% of the participants were aged 35-59 years. Neither sex nor age required data stratification. The established reference intervals were: neutrophil-to-lymphocyte ratio (0.95-3.28), platelet-to-lymphocyte ratio (77.25-213.27), lymphocyte-to-monocyte ratio (2.27-7.17), monocyte-to-lymphocyte ratio (0.14-0.44), derived neutrophil-to-lymphocyte ratio (0.72-2.33), systemic inflammatory response index (0.33-1.89), aggregate index of systemic inflammation (69.85-460.01), and systemic immune-inflammation index (201.64-830.02). CONCLUSION: These reference intervals provide a basis for clinical and epidemiological studies on subclinical inflammation and chronic disease risk.